First of all, I would like to say: Happy new year Haha, this is my first post in 2012 and my first post will began with messages to all admins around the world, to limit their request length. Why? Because it can lead to DOS attack, using a simple POST request with specially crafted messages that can led to huge amount of CPU usages.
I don’t have to explain the background behind it, because many articles has done a great job of explaining. Here’s the related articles explaining the problem:
The most important is the third link, because many sites are using PHP, and so many sites are not yet updated into PHP 5.3, especially shared hosting sites.